Novel nickel-based complex and use thereof in a method for the oligomerisation of olefins

ABSTRACT

The invention describes a novel dissymmetric nickel-based complex and the method of preparation thereof from at least one diphosphinamine ligand B1 of formula (R 1 )(R′ 1 )P—N(R 3 )—P(R 2 )(R′ 2 ), or an iminobisphosphine ligand B2 of formula (R 3 )N═P(R 1 )(R′ 1 )—P(R 2 )(R′ 2 ). The invention also concerns the use of said complex in a method for oligomerisation of olefins.

The invention relates to a novel family of nickel complexes, and methodsof preparation thereof. The invention also relates to the use of saidcomplexes as catalysts in chemical transformation reactions.

PRIOR ART

It is known that nickel-based complexes can be prepared for applicationin various areas of chemistry, particularly in the area of catalytictransformations such as hydroformylation, hydrogenation, cross coupling,oligomerisation of olefins, etc.

Examples of such complexes include the article C.R. Acad. Sci. 1967,C103-106 and the article J. Mol. Catal. A 2001, 169, 19-25 whichdescribe nickel complexes in the presence of monophosphine.

The nickel diphosphinamine complexes described in the prior art aresymmetric and prepared using diphosphinamine ligands in which the twophosphorous atoms are carriers of identical aromatic-type groups (Eur.J. Inorg. Chem., 2009, 3016-3024, Organometallics, 2001, 20, 4769-4771).For example, patent application WO01/10876 describes nickeldiphosphinamine complexes, with the symmetric ligands described beingsubstituted, on the phosphorous, solely by aromatic groups, and used forthe polymerisation of ethylene.

These catalytic systems are relatively inactive in the oligomerisationof ethylene and are generally used for the polymerisation of ethylene.

The applicant has discovered a novel dissymmetric nickel complex,prepared from dissymmetric diphosphinamine or iminobisphosphine ligands,in which one of the phosphorous atoms carries at least one non-aromaticgroup and the other phosphorous atom carries at least one aromaticgroup. It has been discovered that said complexes, whether or not asolvent is present, exhibit improved activity and selectivity forcatalytic transformation reactions, in particular for the catalysis ofolefin oligomerisation or dimerisation reactions.

DETAILED DESCRIPTION OF THE INVENTION

Nickel Complex of Formula (I)

A first object of the invention relates to a novel dissymmetric nickelcomplex of formula (I):

in which

the groups R¹ and R′¹, which may be identical or different, and may ormay not be linked, are selected from the non-aromatic groups,

the groups R² and R′², which may be identical or different, and may ormay not be linked, are selected from the aromatic groups,

R³ is selected from hydrogen, the halogens, the aliphatic hydrocarbongroups, cyclical or not, and which may or may not containheteroelements, and the aromatic groups which may or may not containheteroelements, which may or may not be substituted,

X is an anion or an electron donor, the groups X may or may not belinked, X is selected from hydrogen, the halogens, the aliphatichydrocarbon groups, cyclical or not, and which may or may not containheteroelements, which may or may not be substituted, and the aromaticgroups which may or may not contain heteroelements, which may or may notbe substituted, the olefins, which may or may not containheteroelements, which may or may not be substituted, the borates, thephosphates, the sulphates, the phosphorous ligands which may or may notcontain heteroelements, which may or may not be substituted, the —OR⁴ or—N(R⁵)(R⁶) groups, where R⁴, R⁵ and R⁶ are selected from the aliphatichydrocarbons groups, cyclical, which may or may not containheteroelements, and the aromatic groups which may or may not containheteroelements, which may or may not be substituted,

a is a whole number between 1 and 4, b is a whole number between 0 and6, and c is a whole number between 1 and 4.

The groups R¹ and R′¹ are preferably selected from the non-aromaticgroups and do not contain silicon. R¹ and R′¹ are preferably identical.

The groups R¹ and R′¹ are preferably selected from methyl, ethyl,isopropyl, n-butyl, iso-butyl, tert-butyl, pentyl and cyclohexyl groups,which may or may not be substituted.

The groups R² and R′² are preferably selected from phenyl, o-tolyl,m-tolyl, p-tolyl, mesityl, 3,5-dimethylphenyl, 4-methoxyphenyl,2-methoxyphenyl, 2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl,3,5-di-tert-butyl-4-methoxyphenyl, 3,5-bis(trifluoromethyl)phenyl,benzyl, naphthyl and pyridyl groups, which may or may not besubstituted, and may or may not contain heteroelements. R² and R′² arepreferably identical.

Advantageously, R³ is selected from hydrogen, the alkoxy, aryloxy,sulphur, sulfonamine, sulfonamide, nitro, carbonyl, amino and amidogroups which may or may not comprise aliphatic, cyclical or aromaticgroups, which may or may not contain heteroelements, which may or maynot be substituted.

The complex of formula (I) is advantageously prepared by bringing intocontact a nickel precursor A and at least one diphosphinamine ligand B1of formula (R¹)(R′¹)P—N(R³)—P(R²)(R′²) or an iminobisphosphine ligand B2of formula (R³)N═P(R¹)(R′¹)—P(R²)(R′²) in the presence or not of asolvent, known as a preparation solvent, at a temperature of between−80° C. and +110° C., for a time of between 1 minute and 24 hours.

The nickel precursor A can be selected from nickel(II)chloride,nickel(II)(dimethoxyethane)chloride, nickel(II)bromide,nickel(II)(dimethoxyethane)bromide, nickel(II)fluoride,nickel(II)iodide, nickel(II)sulphate, nickel(II)carbonate,nickel(II)dimethylglyoxime, nickel(II)hydroxide,nickel(II)hydroxyacetate, nickel(II)oxalate, nickel(II)carboxylates suchas 2-ethylhexanoate, for example, nickel(II)phenates, nickel(II)acetate,nickel(II)trifluoroacetate, nickel(II)triflate,nickel(II)acetylacetonate, nickel(II)hexafluoroacetylacetonate,nickel(0)bis(cycloocta-1,5-diene), nickel(0)bis(cycloocta-1,3-diene),nickel(0)bis(cyclooctatetraene), nickel(0)bis(cycloocta-1,3,7-triene),bis(o-tolylphosphito)nickel(0)(ethylene),nickel(0)tetrakis(triphenylphosphite),nickel(0)tetrakis(triphenylphosphine), nickel (0)bis(ethylene),π-allylnickel(II)chloride, π-allylnickel(II)bromide,methallylnickel(II)chloride dimer,η³-allylnickel(II)hexafluorophosphate,η³-methallylnickel(II)hexafluorophosphate, andnickel(II)(1,5-cyclooctadiene) in their hydrated or non-hydrated form,used alone or as a mixture. Said nickel precursors may optionally becomplexed with Lewis bases.

The preparation solvent can be selected from the organic solvents andpreferably from ethers, alcohols, chlorine-containing solvents andsaturated, unsaturated, aromatic or non-aromatic, cyclic or non-cyclichydrocarbons. Said preparation solvent is preferably selected fromhexane, cyclohexane, methylcyclohexane, heptane, butane or isobutane,monoolefins or diolefins preferably containing 4 to 20 carbon atoms,benzene, toluene, ortho-xylene, mesitylene, ethylbenzene,dichloromethane, chlorobenzene, methanol and ethanol, pure or as amixture, and ionic liquids. In the case in which said solvent is anionic liquid, it is advantageously selected from the ionic liquidsdescribed in patents U.S. Pat. No. 6,951,831 B2 and FR 2 895 406 B1.

Preparation of the diphosphinamine ligands B1 of formula(R¹)(R′¹)P—N(R³)—P(R²)(R′²), or iminobisphosphine ligands B2 of formula(R³)N═P(R¹)(R′¹)—P(R²)(R′²) takes place according to methods known fromthe literature (Inorg. Chem. 2003, 2125-2130). The diphosphinamineligands B1 of formula (R¹)(R′¹)P—N(R³)—P(R²)(R′²) can be prepared andisolated by reacting 1 equivalent of chlorophosphine Cl—P(R¹)(R′¹) and 1equivalent of chlorophosphine Cl—P(R²)(R′²) with a primary or aromaticamine R³—NH₂ in the presence of triethylamine. The iminobisphosphineligands B2 of formula (R³)N═P(R¹)(R′¹)—P(R²)(R′²) can be prepared andisolated by reacting a primary or aromatic amine R³—NH₂ and 1 equivalentof chlorophosphine Cl—P(R¹)(R′¹) and 1 equivalent of chlorophosphineCl—P(R²)(R′²) introduced one after the other in the presence oftriethylamine.

Use of the Complex of Formula (I) in a Chemical Transformation Reaction

The nickel complex of formula (I) according to the invention can be usedas a catalyst in a chemical transformation reaction, such as a reactionfor hydrogenation, hydroformylation, cross-coupling or oligomerisationof olefins. In particular, the nickel complex of formula (I) is used ina process for oligomerisation of olefins advantageously comprisingbetween 2 and 10 carbon atoms; preferably in a process of dimerisationof ethylene or propylene.

The nickel complex of formula (I) according to the invention can be usedin the form of a catalytic composition, in a mixture with a compound Cknown as an activating agent. Said activating agent is advantageouslyselected from the group formed by tris(hydrocarbyl)aluminium compounds,chlorine-containing or bromine-containing hydrocarbylaluminiumcompounds, aluminium halides, aluminoxanes, organo-boron compounds, andorganic compounds which are susceptible of donating or accepting aproton, used alone or as a mixture.

The tris(hydrocarbyl)aluminium compounds, the chloride-containing andbromine-containing hydrocarbylaluminium compounds and the aluminiumhalides preferably adhere to the general formula Al_(x)R_(y)W_(z) inwhich R represents a monovalent hydrocarbon radical containing forexample up to 12 carbon atoms such as alkyl, aryl, aralkyl, alkaryl orcycloalkyl, W represents a halogen atom selected for example fromchlorine and bromine, W preferably being a chlorine atom, x takes avalue of between 1 and 2, and y and z take a value of between 0 and 3.Examples of compounds of this type which may be mentioned areethylaluminium sesquichloride (Et₃Al₂Cl₃), methylaluminium dichloride(MeAlCl₂), ethylaluminium dichloride (EtAlCl₂), isobutylaluminiumdichloride (iBuAlCl₂), diethylaluminium chloride (Et₂AlCl),trimethylaluminium, tributylaluminium, tri-n-octylaluminium andtriethylaluminium (AlEt₃).

In the case in which said activating agent is selected fromaluminoxanes, said activating agent is advantageously selected frommethylaluminoxane (MAO), ethylaluminoxane and modifiedmethylaluminoxanes (MMAO). These activating agents may be used alone oras a mixture.

Preferably, said activating agent C is selected fromdichloroethylaluminium (EtAlCl₂) and methylaluminoxane (MAO).

In the case in which said activating agent is selected from organo-boroncompounds, said activating agent is preferably selected from Lewis acidsof the tris(aryl)borane type, such as tris(perfluorophenyl)borane,tris(3,5-bis(trifluoromethyl)phenyl)borane,tris(2,3,4,6-tetrafluorophenyl)borane, tris(perfluoronaphtyl)borane,tris(perfluorobiphenyl)borane and their derivatives and (aryl)boratesassociated with a triphenylcarbenium cation, or a trisubstitutedammonium cation such as triphenylcarbeniumtetrakis(perfluorophenyl)borate, N,N-dimethylaniliniumtetrakis(perfluorophenyl)borate, N,N-diethylaniliniumtetrakis(3,5-bis(trifluoromethyl)phenyl)borate, or triphenylcarbeniumtetrakis(3,5-bis(trifluoromethyl)phenyl)borate.

In the case in which said activating agent is selected from organiccompounds which are susceptible of donating a proton, said activatingagent is preferably selected from acids with formula HY in which Yrepresents an anion.

In the case in which said activating agent is selected from organiccompounds which are susceptible of accepting a proton, said activatingagent is preferably selected from Brönsted bases.

The nickel complex of formula (I) according to the invention or thecatalytic composition containing it is advantageously used in a processof oligomerisation or dimerisation of olefins, preferably in a processof dimerisation of ethylene or propylene.

The solvent for the oligomerisation or dimerisation process may beselected from organic solvents, and preferably from ethers, alcohols,chlorine-containing solvents and saturated, unsaturated, aromatic ornon-aromatic, cyclic or non-cyclic hydrocarbons. In particular, saidsolvent is selected from hexane, cyclohexane, methylcyclohexane,heptane, butane or isobutane, monoolefins or diolefins preferablycontaining 4 to 20 carbon atoms, benzene, toluene, ortho-xylene,mesitylene, ethylbenzene, dichloromethane, chlorobenzene, methanol andethanol, pure or as a mixture, and ionic liquids.

In the case in which said reaction solvent is an ionic liquid, it isadvantageously selected from the ionic liquids described in patents U.S.Pat. No. 6,951,831 B2 and FR 2 895 406 B1.

Oligomerisation is defined as the transformation of a monomer unit intoa compound or mixture of compounds with general formula C_(p)H_(2p),with 4≦p≦80, preferably with 4≦p≦50, more preferably with 4≦p≦26 andhighly preferably with 4≦p≦14.

The olefins used in the oligomerisation or dimerisation process areolefins containing 2 to 10 carbon atoms. Preferably, said olefins areselected from ethylene, propylene, n-butenes and n-pentenes, alone or asa mixture, pure or diluted.

In the case in which said olefins are diluted, said olefins are dilutedwith one or more alkane(s) such as those found in “cuts” obtained fromoil refining processes such as catalytic cracking or steam cracking.

Preferably, the olefin used in the oligomerisation or dimerisationprocess is ethylene or propylene.

Said olefins may be obtained from non-fossil sources such as biomass. Asan example, the olefins used in the oligomerisation process according tothe invention may be produced from alcohols, in particular bydehydration of alcohols.

The concentration of nickel in the catalytic solution is advantageouslyin the range 1×10⁻⁸ to 1 mol/l, and more preferably in the range 1×10⁻⁶to 1×10⁻² mol/l.

The molar ratio between the activating agent C and the nickel precursoris advantageously between 1/1 and 10,000/1, preferably between 1/1 and1,000/1 for the aluminoxanes and preferably between 1/1 and 100/1 forthe other aluminium derivatives and the other Lewis acids.

The oligomerisation or dimerisation process is advantageously operatedat a total pressure in the range between atmospheric pressure and 20MPa, preferably in the range between 0.5 and 8 MPa, and a temperature inthe range −40 to +250° C., preferably in the range −20° C. to 150° C.

The heat generated by the reaction can be eliminated by all means knownto a person skilled in the art.

The oligomerisation or dimerisation process can be carried out in aclosed system, in a semi-open system or continuously, with one or morereaction stages. Vigorous agitation is advantageously implemented toensure a good contact between the reagent(s) and the catalyticcomposition.

The oligomerisation or dimerisation process can be implemented in adiscontinuous manner. In this case, the solution comprising the complexaccording to the invention is introduced into a reactor fitted with thenormal agitation, heating and cooling devices.

The oligomerisation or dimerisation process can also be implemented in acontinuous manner. In this case, the solution comprising the complexaccording to the invention is injected at the same time as the olefininto a reactor agitated by conventional mechanical means or by externalrecirculation, and maintained at the desired temperature.

The catalytic composition is destroyed by any normal means known to aperson skilled in the art, then the reaction products and the solventare separated, for example by distillation. The olefin that has not beentransformed can be recycled in the reactor.

The method according to the invention can be implemented in a reactorwith one or more reaction stages in series, the olefin feed and/or thecatalytic composition pre-conditioned in advance being introducedcontinuously, either in the first stage, or in the first and any otherof the stages. Upon leaving the reactor, the catalytic composition canbe deactivated, for example by injection of ammonia and/or an aqueoussolution of soda and/or an aqueous solution of sulphuric acid.Unconverted olefins and any alkanes present in the feed are thenseparated from the oligomers by distillation.

The products of this process may have an application, for example, ascomponents of fuels for motor vehicles, as feeds in a hydroformylationprocess for the synthesis of aldehydes and alcohols, as components forthe chemical, pharmaceutical or perfume industries and/or as feeds in ametathesis process for synthesis of propylene, for example.

The following examples illustrate the invention without limiting itsscope. The notation “Cy” represents the tricyclohexyl group.

EXAMPLE 1

Synthesis of Ligands

Iminobisphosphine ligands R′—SO₂—N═P(R¹)(R′¹)—P(R²)(R′²) were preparedand isolated by reacting a sulfonamide and 2 equivalents ofchlorophosphine (which may be identical or different) in the presence oftriethylamine. Examples are provided by ligands 1 and 2 in whichR¹═R′¹═R²═R′² (comparative examples) and ligands 3 and 4 in which R¹═R′¹and R²═R′² and R¹ is different from R². The structures of the fourligands are shown below.

Synthesis of the Ligand 1:(4-bromo-N-(1,1,2,2-tetraphenyldiphosphanylidene)benzenesulfonamide)

Freshly distilled chlorodiphenylphosphine (0.760 ml, 4.24 mmol, 2 eq.)was added drop by drop to a solution of 4-bromobenzenesulfonamide (500mg, 2.12 mmol, 1 eq.) and triethylamine (1.6 ml, 11.2 mmol, 5.3 eq.) inTHF (10 ml) at ambient temperature and under vigorous agitation. Onceaddition was complete, the mixture was agitated for 5 minutes and thenthe suspension was filtered under a nitrogen atmosphere on a sinteredglass filter. Evaporation of the solvent and the volatile components ledto the formation of a solid. This solid was dissolved in a minimum ofdichloromethane, then pentane (20 ml) was added. By evaporating thissolution, a precipitate appeared. The supernatant was removed using asyringe and the solid was then washed with pentane (2×10 ml) and driedunder a vacuum to provide ligand 1 in the form of a white powder(isolated yield: 68%).

¹H NMR (300 MHz, CD₂Cl₂): δ 7.82-6.89 (m, 24H). ³¹P NMR (121 MHz,CD₂Cl₂) 19.72 (d, J=281.1 Hz), −18.74 (d, J=281.1 Hz).

³¹P{¹H} NMR (121 MHz, CD₂Cl₂): 19.72 (d, J=279.9 Hz), −18.74 (d, J=281.2Hz).

MS (FAB+): m/z calc. for C₃₀H₂₅NO₂P₂BrS ([MH]⁺): 606.0248; obs.:606.0255.

Synthesis of Ligand 2:(4-butyl-N-(1,1,2,2-tetraphenyldiphosphanylidene)benzenesulfonamide)

Freshly distilled chlorodiphenylphosphine (0.840 ml, 4.68 mmol, 2 eq.)was added drop by drop to a solution of 4-butylbenzenesulfonamide (500mg, 2.34 mmol, 1 eq.) and triethylamine (1 ml, 7.17 mmol, 3 eq.) in THF(20 ml), at ambient temperature and under vigorous agitation. Onceaddition was complete, the mixture was agitated for 5 minutes and thenthe suspension was filtered under a nitrogen atmosphere on a sinteredglass filter. Evaporation of the solvent and the volatile components ledto the formation of an oil. This oil was solubilised in diethyl ether(10 ml) and the solution evaporated. This step was repeated 4 timesuntil the product precipitated. The solid was then dried under a vacuumto provide ligand 2 in the form of a white powder (isolated yield: 79%).

¹H NMR (300 MHz, CD₂Cl₂): δ 7.91-6.33 (m, —CH_(Ar), 24H), 2.59 (t,CH₃—CH₂—CH₂—CH₂—CAr, J=7.7 Hz, 2H), 1.57 (m, CH₃—CH₂—CH₂—CH₂—CAr, 2H),1.33 (m, CH₃—CH₂—CH₂—CH₂—Car, 2H), 0.93 (t, CH₃—CH₂—CH₂—CH₂—Car, J=7.3Hz, 3H).

³¹P NMR (121 MHz, CD₂Cl₂): δ 19.47 (d, J=277.9 Hz), −17.90 (d, J=278.0Hz).

MS (FAB+): m/z calc. for C₃₄H₃₄O₂NP₂S ([M+H]⁺): 582.1786; obs.: 582.1790

Synthesis of N-diphenylphosphino-4-butylbenzenesulfonamide

Freshly distilled chlorodiphenylphosphine (9.38 mmol, 1 eq.) was addeddrop by drop to a solution of 4-butylbenzene-1-sulfonamide (9.38 mmol, 1eq.) and triethylamine (25 mmol) in THF (20 ml), at ambient temperatureand under vigorous agitation. The suspension was left under agitationfor one night at ambient temperature. Evaporation of the solvent and thevolatile components led to the formation of a solid. This solid wasdissolved in 10 ml of dichloromethane, and then pentane (40 ml) wasadded, with the appearance of a precipitate. The supernatant was removedusing a syringe and the solid was then washed with pentane (2×20 ml) anddried under a vacuum to provideN-diphenylphosphino-4-butylbenzenesulfonamide in the form of a whitepowder. This compound could be isolated and purified or used directly inanother stage of synthesis (isolated yield: 74%).

Synthesis of Ligand 3:4-butyl-N-(1,1-diisopropyl-2,2-diphenyldiphosphanylidene)benzenesulfonamide

Diisopropylchlorophosphine (0.746 ml, 4.68 mmol, 1 eq.) was added dropby drop to a solution of N-diphenylphosphino-4-butylbenzenesulfonamide(1.86 g, 4.68 mmol, 1 eq.) and triethylamine (1.30 ml, 9.36 mmol, 2 eq.)in THF (20 ml), at ambient temperature and under vigorous agitation.Once addition was complete, the mixture was agitated for 10 minutes andthen the suspension was filtered under a nitrogen atmosphere on asintered glass filter. Evaporation of the solvent and the volatilecomponents led to the formation of an oil. Pentane (20 ml) was added tothis oil, then following trituration the pentane was removed using asyringe. The oil was then suspended in pentane (10 ml) and the solutionevaporated under a vacuum. This step was repeated once with pentane andthen twice with diethyl ether (10 ml) allowing the formation of a solid.The solid was washed with pentane (2×10 ml) then dried under a vacuum toprovide ligand 3 in the form of a white solid (isolated yield: 34%).

¹H (300 MHz, CD₂Cl₂): δ: δ 7.98-7.83 (m, 4H, —PPh₂), 7.76-7.64 (m, 2H,—CH₂—Ar—SO₂), 7.60-7.35 (m, 6H, —PPh₂), 7.23-7.12 (m, 2H, —CH₂—Ar—SO₂),2.69-2.57 (t, 2H, J=7.4 Hz, CH₃—CH₂—CH₂—CH₂—Ar), 2.44 (m, 2H,CH₃—CH—CH₃), 1.69-1.48 (m, 2H, CH₃—CH₂—CH₂—CH₂—Ar), 1.35 (m, 2H,CH₃—CH₂—CH₂—CH₂—Ar), 1.18-0.99 (m, 12H, CH₃—CH—CH₃), 0.93 (t, J =7.3 Hz,3H, CH₃—CH₂—CH₂—CH₂—Ar).

³¹P (121 MHz, CD₂Cl₂) δ: 20.13 (d, J=311.6 Hz); 2.80 (d, J=311.6 Hz).

Synthesis of Ligand 4:4-butyl-N-(1,1-dicyclohexyl-2,2-diphenyldiphosphanylidene)benzenesulfonamide

Dicyclohexylylphosphine (0.200 ml, 0.91 mmol, 1 eq.) was added drop bydrop to a solution of N-diphenylphosphino-4-butylbenzenesulfonamide(0.361 g, 0.91 mmol, 1 eq.) and triethylamine (0.126 ml, 1.82 mmol, 2eq.) in THF (10 ml), at ambient temperature and under vigorousagitation. Once addition was complete, the mixture was agitated for 5minutes and then the suspension was filtered under a nitrogen atmosphereon a sintered glass filter. Evaporation of the solvent and the volatilecomponents led to the formation of an oil. Pentane (10 ml) was added tothis oil, then following trituration it was evaporated under a vacuum.This step was repeated once with pentane and then twice with diethylether (10 ml) allowing the formation of a solid. The solid was driedunder a vacuum to provide ligand 4 in the form of a white solid(isolated yield: 51%).

¹H NMR (300 MHz, CD₂Cl₂): δ 7.90 (dd, J =12.5, 7.6 Hz, 4H, PPh₂),7.78-7.67 (dd, J =8.4, 2.0 Hz, 2H, Ar—SO₂), 7.61-7.40 (m, 6H, PPh₂),7.18 (dd, J=8.4, 2.0 Hz, 2H, Ar—SO₂), 2.63 (t, J=7.6 Hz, 2H, —CH₂—Ar),2.30-2.01 (m, 2H, Cy), 1.81 (m, 2H, Cy), 1.73-1.49 (m, 8H, Cy),1.73-1.49 (m, 2H, —CH₂—CH₂—Ar) 1.33 (dt, J=16.3, 7.3 Hz, 2H,—CH₂—CH₂—CH₂—Ar), 1.17 (m, 10H, Cy), 0.93 (t, J=7.3 Hz, 3H,H₃C—CH₂—CH₂).

³¹P NMR (121 MHz, CD₂Cl₂): δ 20.44 (d, J=314.9 Hz), −4.98 (d, J=314.4Hz).

MS (FAB+): m/z calcd. For C₃₄H₃₄O₂NP₂S ([M+H]⁺): 594.2725; obsd.:594.2732.

Synthesis of the Nickel Complexes

The ligands 1, 2, 3 and 4 were reacted with NiBr₂(dme) to provide thecomplexes 5, 6, 7 and 8. Complex 9 is a reference complex.

Synthesis of Complex 5 (Comparative)

4-bromo-N-(1,1,2,2-tetraphenyldiphosphanylidene)benzenesulfonamide 1(200 mg, 0.331 mmol, 1.01 eq.) and nickel(II)(dimethoxyethane)bromide(101 mg, 0.327 mmol, 1 eq.) were suspended in toluene (3 ml). Thesuspension was agitated at 60° C. for 2 hours. Following cooling, thesolvent was removed using a syringe and the solid washed three timeswith pentane (5 ml) and then dried under a vacuum to provide complex 5in the form of a reddish-brown powder (isolated yield: 80%). The productwas analysed by mass, proton and phosphorus NMR.

¹H NMR (300 MHz, CD₂Cl₂): δ 8.16 (m, 8H, PPh₂), 7.76 (t, J=7.3 Hz,4H_(para)), 7.59 (m, 8H, PPh₂), 7.06 (d, J=8.2 Hz, 2H, —Ar—SO₂), 6.18(d, J=8.5 Hz, 2H, —Ar—SO2).

³¹P NMR (121 MHz, CD₂Cl₂): δ 65.52. ³¹P{¹H} NMR (121 MHz, CD₂Cl₂) δ 665.52.

MS (FAB+): m/z calc. for C₃₀H₂₄NO₂P₂Br₂SNi ([M-HBr]⁺): 741.8701; obs.:741.8702.

Synthesis of Complex 6 (Comparative)

4-butyl-N-(1,1,2,2-tetraphenyldiphosphanylidene)benzenesulfonamide 2(200 mg, 0.344 mmol, 1 eq.) and nickel(II)(dimethoxyethane)bromide (106mg, 0.344 mmol, 1 eq.) were suspended in toluene (3 ml). The suspensionwas agitated at 65° C. for 1 h until formation of a red solid. Followingcooling, the solvent was removed using a syringe and the solid waswashed three times with pentane (5 ml) and then dried under a vacuum toprovide complex 6 in the form of a reddish-brown powder (isolated yield:68%). The product was analysed by proton and phosphorous NMR.

¹H NMR (300 MHz, CD₂Cl₂): δ 8.91-5.91 (m, H_(Ar), 24H), 2.72-2.24 (m,CH₃—CH₂—CH₂—CH₂—CAr 2H), 1.51 (m, CH₃—CH₂—CH₂—CH₂—CAr, 2H), 1.31 (m,CH₃—CH₂—CH₂—CH₂—CAr 2H), 0.95 (m, CH₃—CH₂—CH₂—CH₂—CAr 3H).

³¹P NMR (121 MHz, CD₂Cl₂) δ 64.10. ³¹P{¹H} NMR (121 MHz, CD₂Cl₂) δ64.07.

Synthesis of Complex 7

4-butyl-N-(1,1-diisopropyl-2,2-diphenyldiphosphanylidene)benzenesulfonamide3 (400 mg, 0.786 mmol, 1 eq.) and nickel(II)(dimethoxyethane)bromide(266 mg, 0.864 mmol, 1.1 eq.) were suspended in dichloromethane (5 ml)at ambient temperature for two hours. The solution was filtered on asintered glass filter and the filtrate evaporated under a vacuum. Thesolid was washed three times with pentane (10 ml) and dried under avacuum to provide complex 7 in the form of a red powder (isolated yield:61%).

¹H NMR (300 MHz, CD₂Cl₂): δ 8.77-6.21 (m, 14H, Ar), 3.29 (m, 4H,CH_(3—)CH—CH₃ and —CH₂—Ar), 2.43 (m, 2H, CH₂—CH₂—Ar), 1.66-1.00 (m, 14H,CH_(3—)CH—CH₃ and CH₃—CH₂—CH₂—CH₂—Ar), 0.78 (t, J=7.8 Hz, 3H,CH₃—CH₂—CH₂—CH₂—Ar).

³¹P NMR (121 MHz, CDCl₃) δ 116.96 (d, J=119.0 Hz), 62.84 (d, J=119.4Hz).

³¹P{¹H} NMR (121 MHz, CDCl₃) δ 116.92 (d, J=116.5 Hz), 62.84 (d, J=117.6Hz).

Synthesis of Complex 8

4-butyl-N-(1,1-dicyclohexyl-2,2-diphenyldiphosphanylidene)benzenesulfonamide4 (98 mg, 0.165 mmol, 1.02 eq.) and nickel(II)(dimethoxyethane)bromide(50 mg, 0.162 mmol, 1 eq.) were suspended in dichloromethane at ambienttemperature for two hours. The solution was filtered on a sintered glassfilter and the filtrate evaporated under a vacuum. The solid was washedthree times with pentane (5 ml) and dried under a vacuum to providecomplex 8 in the form of a red powder (isolated yield: 54%). Crystals ofcompound 8 were obtained by slow diffusion of pentane in a solution of 8in toluene and dichloromethane. The product was analysed by mass,phosphorous NMR and X-ray diffraction.

³¹P NMR (121 MHz, CD2Cl2) δ 108.15 (d, J=118.6 Hz), 60.28 (d, J=119.2Hz). MS (FAB+): m/z calc. for C₃₄H₄₅Br₂NO₂P₂SNi ([M]⁺): 811.0354; obs.:811.0337.

EXAMPLE 2 Oligomerisation of Ethylene

The ethylene oligomerisation reaction was evaluated with nickelcomplexes 5 and 6 and 7 in the presence of methylaluminoxane (MAO) at45° C. and under 30 bar of ethylene (1 bar=0.1 MPa)

Operating conditions: The 100 ml reactor was dried under a vacuum at100° C. for 2 hours and pressurised with ethylene. The catalyst wasintroduced (0.1 mmol in 8 ml of toluene) followed by methylaluminoxane(2 ml, 10% in toluene, 300 eq.). The temperature and the pressure wereset at 45° C. and 35 bar. Agitation was commenced (t=0). After the setreaction time, the reactor was cooled to ambient temperature anddepressurised under agitation. The liquid phase was neutralised withaqueous H₂SO₄ and analysed by GC.

Complexes 5 and 6 activated by MAO (300 eq.) were considered to beinactive, as the consumption of ethylene was negligible. Complex 7,activated by MAO was highly active in the oligomerisation of ethylene(>10⁷ g_(C2H4)/(mol_(Ni).h)) and no polymer was formed. The GC analysesconfirmed that the products formed were principally butenes and hexenes.The results are shown in Table 1.

TABLE 1 Oligomerisation of ethylene catalysed by 5, 6, 7.^(a) Time Cons.C₂H₄ Distribution by oligomers [wt. %] Entry Complex (min.) (g)Activity^(b) C4^(c) C6^(c) C8^(+c) 1-C4^(d) 2-C4^(d) 1^(e) 5 22 N.d.^(f)— — — — — — 2^(e) 6 20 N.d.^(f) — — — — — — 3  7 14 31.5 14.10⁶ 60.325.7 14.0 6.6 93.4 ^(a)Reaction conditions: n_(ni) =10 μmol,co-catalyst: MAO (300 eq.), 30 bar C₂H₄, 45° C., solvent: toluene (10ml). ^(b)g_(C2H4)/(mol_(Ni) · h). ^(c)Determined by GC, wt. %/alloligomers. ^(d)wt. %/to the other products of cut C4. ^(e)Comparativeexamples. ^(f)Not determined: ethylene consumption negligible,activities observed <0.7 · 10⁶.

Dissymmetric complex 7 led to performances that were far superior interms of activity to symmetric complexes 5 or 6.

EXAMPLE 3 Oligomerisation of Propylene

The oligomerisation of propylene was performed with two differentactivating agents: EADC (ethylaluminium dichloride) and MAO(methylaluminoxane). The tests performed with catalyst 9 NiCl₂(PCy₃)₂are reference tests.

Tests with EADC

Operating conditions: The 250 ml reactor was dried under a vacuum at100° C. for 2 hours, cooled to 10° C. and then filled with propylene(pressure of 1.4 bar). 33 ml of chlorobenzene and 10 ml of n-heptane(accurately weighed internal standard) were then introduced, followed by8 g of propylene. The reactor was cooled to −10° C. under agitation. TheEADC (ethylaluminium dichloride, 0.075 M in toluene, 15 eq., 2 ml)activating agent was then injected, followed by the catalyst (0.1 mmolin 5 ml of chlorobenzene). 12 g of propylene were then introduced.Agitation was then commenced (t=0). The temperature was maintained at−10° C. for 10 minutes and then smoothly increased to 10° C. Theconsumption of propylene was followed by a reduction in pressure. Theliquid phase was then removed and neutralised with aqueous NaOH. Theorganic phase was weighed and analysed by a GC fitted with a cryostat.The results are shown in Table 2.

Following activation with the EADC activating agent, complexes 7, 8 and9 were highly active for the oligomerisation of propylene at 10° C. TheC6 selectivity of complexes 7 and 8 was superior to the referencecomplex 9. The 1-dimethylbutene and 2-dimethylbutene selectivity wasapproximately 25% for activated complexes 7 and 8.

TABLE 2 Oligomerisation of propylene with different complexes activatedby the EADC activating agent.^(a) Com- Time Distribution by oligomers[wt. %]^(c) Entry plex (min.) Activity^(b) C6 C9 C12 C15+  1^(d) 6 54Inactive 2 7 30 4 96.8 2.9 0.2 0.1 3 8 5 24 97.1 2.3 0.2 0.4  4^(d) 9 422.9 86.4 12.1 1.3 0.2 ^(a)Reaction conditions: n_(ni) = 10 μmol,co-catalyst: EADC (15 eq.), 20 g C₃H₆, 10° C., solvent: chlorobenzene(50 ml). ^(b)10⁶ g_(oligo) · mol_(Ni) ^(−h) · h⁻¹. ^(c)Determined by GCwith n-heptane as internal standard. ^(d)Comparative example.

The dimer selectivity obtained with complexes 7, 8 and 9 activated withthe EADC activating agent is shown in Table 3.

TABLE 3 dimer selectivity Entry Complex 4M1P 1-DMB 4M2P 2M1P 2M2P Hex2-DMB 2 7 1.2 23.7 35.5 13 13.4 11.4 1.8 3 8 1.1 17.3 43.3 12.4 11 13.61.3  4^(a) 9 6.6 62.2 10.9 17.2 0.5 2.4 0.2 Dimer selectivity in wt. %,determined by GC. 4M1P: 4-methylpentene-1, 1-DMB: 2,3-dimethylbutene-1,4M2P: 4-methylpentene-2, 2M1P: 2-methylpentene-1, 2M2P:2-methylepentene-2, Hex: linear hexenes, 2-DMB: 2,3-dimethylbutene-2.^(a)Comparative examples.

Tests with MAO

Operating conditions: The 250 ml reactor was dried under a vacuum at100° C. for 2 hours, cooled to 10° C. and then filled with propylene(pressure of 1.4 bar). 33 ml of chlorobenzene and 10 ml of n-heptane(accurately weighed internal standard) were then introduced, followed by4 g of propylene. The co-catalyst MAO (1.5 M in toluene, 300 eq., 2 ml)was then injected followed by the catalyst (0.1 mmol in 5 ml ofchlorobenzene). 16 g of propylene were then introduced. Agitation wasthen commenced (t=0). The temperature was maintained at 10° C. for 10minutes and was then smoothly increased to 45° C. The consumption ofpropylene was followed by a reduction in pressure. The liquid phase wasthen removed and neutralised with aqueous H₂SO₄. The organic phase wasweighed and analysed by a GC fitted with a cryostat. The results areshown in Table 4.

Following activation with MAO, complexes 7, 8 and 9 were active foroligomerisation of propylene at 45° C. The C6 selectivity of complexes 7and 8 was superior to reference complex 9. The 1-dimethylbutene and2-dimethylbutene (DMB 1 and 2) selectivity was 40.7% and 47.8% foractivated complexes 7 and 8, respectively.

TABLE 4 Oligomerisation of propylene with different complexes activatedby MAO.^(a) Distribution by oligomers [wt. %]^(b) Entry Complex C6 C9C12 C15+ 1 7 81.3 12.3 3.9 2.5 2 8 80.1 14 4.3 1.6  3^(c) 9 56.5 23.310.8 9.4 ^(a)Reaction conditions: n_(ni) = 10 μmol, co-catalyst: MAO(300 eq.), 10° C., 20 g C₃H₆, solvent: chlorobenzene (50 ml), reactiontime: 110 min, total conversion. ^(b)Determined by GC with n-heptane asinternal standard. ^(c)Comparative examples.

The dimer selectivity obtained with complexes 7, 8 and 9 activated withMAO activating agent is shown in Table 5.

TABLE 5 Dimer selectivity. Entry Complex 4M1P 1-DMB 4M2P 2M1P 2M2P Hex2-DMB 1 7 1.9 37.9 11.8 25.3 13.9 6.4 2.8 2 8 1.8 44.7 7.8 25.5 12.3 4.83.1  3a 9 0.6 72.8 6.3 12.9 4.1 2.4 0.9 Dimer selectivity in wt. %,determined by GC. 4M1P: 4-methylpentene-1, 1-DMB: 2,3-dimethylbutene-1,4M2P: 4-methylpentene-2, 2M1P: 2-methylpentene-1, 2M2P:2-methylepentene-2, Hex: linear hexenes, 2-DMB: 2,3-dimethylbutene-2.aComparative examples.

The above examples show that the catalytic complexes of the methodaccording to the invention have an improved activity and selectivity forthe oligomerisation of olefins comprising preferably between 2 and 10carbon atoms, more specifically for the dimerisation of olefinscomprising between 2 and 10 carbon atoms.

1. Dissymmetric nickel complex of formula (I):

in which the groups R¹ and R′¹, which may be identical or different, andmay or may not be linked, are selected from the non-aromatic groups, thegroups R² and R′², which may be identical or different, and may or maynot be linked, are selected from the aromatic groups, R³ is selectedfrom hydrogen, the halogens, the aliphatic hydrocarbon groups, cyclicalor not, and which may or may not contain heteroelements, and thearomatic groups which may or may not contain heteroelements, which mayor may not be substituted, X is an anion or an electron donor, thegroups X may or may not be linked, X is selected from hydrogen, thehalogens, the aliphatic hydrocarbon groups, cyclical or not, and whichmay or may not contain heteroelements, which may or may not besubstituted, and the aromatic groups which may or may not containheteroelements, which may or may not be substituted, the olefins, whichmay or may contain heteroelements, which may or may not be substituted,the borates, the phosphates, the sulphates, the phosphorous ligandswhich may or may not contain heteroelements, which may or may not besubstituted, the —OR⁴ or —N(R⁵)(R⁶) groups, where R⁴, R⁵ and R⁶ areselected from the aliphatic hydrocarbons groups, cyclical, which may ormay not contain heteroelements, the aromatic groups which may or may notcontain heteroelements, which may or may not be substituted, a is awhole number between 1 and 4, b is a whole number between 0 and 6, and cis a whole number between 1 and
 4. 2. Complex according to claim 1 inwhich the groups R¹ and R′¹ are selected from the non-aromatic groupsnot containing silicon.
 3. Complex according to claim 1 in which thegroups R¹ and R′¹ are selected from methyl, ethyl, isopropyl, n-butyl,iso-butyl, tert-butyl, pentyl, cyclohexyl groups, which may or may notbe substituted or unsubstituted.
 4. Complex according to claim 1 inwhich the groups R² and R′² are selected from phenyl, o-tolyl, m-tolyl,p-tolyl, mesityl, 3,5-dimethylphenyl, 4-methoxyphenyl, 2-methoxyphenyl,2-isopropoxyphenyl, 4-methoxy-3,5-dimethylphenyl,3,5-ditert-butyl-4-methoxyphenyl, 3,5-bis(trifluoromethyl)phenyl,benzyl, naphthyl and pyridyl, which may or may not be substituted andwhich may or may not contain heteroelements.
 5. Method of preparation ofthe complexes according claim 1 comprising bringing into contact anickel precursor A and at least one diphosphinamine ligand B1 of formula(R¹)(R′¹)P—N(R³)—P(R²)(R′²) or at least one iminobisphosphine ligand B2of formula (R³)N═P(R¹)(R′¹)—P(R²)(R′²) in the presence or not of asolvent, R¹, R′¹, R², R′² and R³ meeting the specifications according toclaim
 1. 6. Method of preparation according to claim 5 implemented at atemperature of between −80° C. and +110° C., for a period of between 1minute and 24 hours.
 7. Method of preparation according to claim 5 inwhich the nickel precursor A is selected from nickel(II)chloride,nickel(II)(dimethoxyethane)chloride, nickel(II)bromide,nickel(II)(dimethoxyethane)bromide, nickel(II)fluoride,nickel(II)iodide, nickel(II)sulphate, nickel(II)carbonate,nickel(II)dimethylglyoxime, nickel(II)hydroxide,nickel(II)hydroxyacetate, nickel(II)oxalate, nickel(II)carboxylates suchas 2-ethylhexanoate, for example, nickel(II)phenates, nickel(II)acetate,nickel(II)trifluoroacetate, nickel(II)triflate,nickel(II)acetylacetonate, nickel(II)hexafluoroacetylacetonate,nickel(0)bis(cycloocta-1,5-diene), nickel(0)bis(cycloocta-1,3-diene),nickel(0)bis(cyclooctatetraene), nickel(0)bis(cycloocta-1,3,7-triene),bis(o-tolylphosphito)nickel(0)(ethylene),nickel(0)tetrakis(triphenylphosphite),nickel(0)tetrakis(triphenylphosphine), nickel(0)bis(ethylene),π-allylnickel(II)chloride, π-allylnickel(II)bromide,methallylnickel(II)chloride dimer,η³-allylnickel(II)hexafluorophosphate,η³-methallylnickel(II)hexafluorophosphate, andnickel(II)(1,5-cyclooctadiene) in their hydrated or non-hydrated form,used alone or as a mixture. Said nickel precursors may optionally becomplexed with Lewis bases.
 8. Method of oligomerisation of a feed ofolefins comprising bringing said feed into contact with the complexaccording to claim 1, whether or not a solvent is present.
 9. Methodaccording to claim 8 in which the complex is used in a mixture with acompound C selected from the group formed by tris(hydrocarbyl)aluminiumcompounds, chlorine-containing or bromine-containinghydrocarbylaluminium compounds, aluminoxanes, organo-boron compounds,and organic compounds which are susceptible of donating or accepting aproton, used alone or as a mixture.
 10. Method according to claim 8 inwhich the olefins are selected from ethylene, propylene, the n-butenesand the n-pentenes, used alone or in a mixture, pure or diluted. 11.Method according to claim 8 in which the nickel is present in aconcentration of between 1×10⁻⁸ and 1 mol/l.
 12. Method according toclaim 8 in which a total pressure is operated at in the range betweenatmospheric pressure and 20 MPa, and at a temperature in the range −40°C. to +250° C.
 13. Method according to claim 8 in which the reaction isa dimerisation reaction.
 14. Method according to claim 13 in which thereaction is an ethylene or propylene dimerisation reaction.